Harriette Thompson, 92, became the oldest woman to complete a marathon after she ran 26.2 miles to pass the finish line at the Rock ‘n’ Roll Marathon in San Diego on Sunday. Thompson, a former concert pianist and a cancer survivor, started running at the age of 76. She has, so far, participated in 16 marathons to help raise money for cancer research.

"Every year I write to my friends and say, this is my last year," she said. "And then I do another one."

This year Harriette ran for her son, a captain in the Navy who was recently diagnosed with cancer, and raised money for the Leukemia Lymphoma Society. A two-time cancer survivor herself, Harriette suffered the loss of her husband and struggled through a staph infection in her legs while training for this year's race.

How does she get through the 26.2 miles? A classically trained pianist who played three times at Carnegie Hall, Thompson says she mentally plays old piano pieces she had performed.

"I just don't think of myself being that unusual," she said. "I have a lot of people saying what an inspiration I am. That's nice to hear, good for something at this age."